1. Field of The Invention
This invention relates to electronic fuel injection systems and more particularly to a dual mode hybrid control system for operating electronic fuel injection systems so as to achieve an optimal compromise between engine emissions, fuel economy and driveability.
2. Description of The Prior Art
The ever-increasing number of automobiles on our streets and highways, particularly in urban areas, has caused a growing concern because of the pollution caused in part by automobile exhaust fumes. This has led to increased emphasis on ways for reducing undesirable exhaust emissions such as unburned hydrocarbons, carbon monoxide and nitrous oxides. Acting on this concern, the government has established increasingly stringent requirements for improved control of air/fuel ratios for automobile engines in an attempt to reduce or eliminate harmful exhaust emissions.
The air/fuel ratio of an internal combustion engine, i.e. the amount of air drawn into a engine in relation to the amount of fuel supplied thereto, ideally should be maintained at values which, for all possible phases of engine operation, will prevent or eliminate exhaust emissions of unburned fuel and other by-products of combustion from exceeding predetermined levels. If the air/fuel ratio is less than that value which will present an amount of fuel which will be essentially completely consumed during combustion, then a wasteful surplus of fuel together with undesirable products of incomplete combustion will be discharged into the atmosphere through the engine's exhaust system in the form of pollution.
One of the most commercially feasible means for reducing emissions is the well-known three-way catalyst which greatly reduces exhaust emissions. The three-way catalyst has the best conversion efficiency of hydrocarbons, carbon monoxide and nitrous oxide when the engine is operating in a narrow window of air/fuel ratios near the stoichiometric air/fuel ratio.
However, a more recent problem thought to be at least as important by many members of our society, concerns the alarming fuel shortage existing in the world today and our need to conserve fuel and operate at peak fuel efficiency. It has been found, however, that for best fuel economy, the air/fuel ratio is required to be leaned out to the general range of 16 to 1 to 18 to 1. Furthermore, good drivability requires that the air/fuel ratio be set relatively rich during acceleration operation. Therefore, we are faced with the dilemma of having to chose between maximum reduction of engine emissions, maximum fuel economy, or optimal or at least acceptable drivability.
Most of the techniques of the prior art for controlling air/fuel ratios have addressed only one of these problems. Various complex mechancal and electrical means have been devised to substantially reduce engine emissions. Still other complex mechanical and electrical systems have been devised in an attempt to improve fuel economy. Most of these systems are extremely complex, expensive, mechancally prone to malfunction or fail and do not attempt to address the several critical problems which must be faced in today's society.
Those of the prior art who have recognized even some aspects of these problems have employed extremely expensive and complex computer controlled systems and the like in an attempt to solve these many faceted problems. Such solutions are not commercially feasible. None of the prior art patents have produced a commercially feasible, relatively simple, inexpensive system for obtaining an optimal compromise between engine emissions, fuel economy and drivability.
The present invention avoids the difficulties of the prior art and provides a relatively inexpensive, mechanically simple, failure-free, dual mode control circuit for operating an electronic fuel injection system so as so achieve an optimal compromise between engine emissions, fuel economy and drivability.